To be honest no - I've never done that, nor have I seen someone do that. It would definitely increase PR level (and possible bugs and/or missing specs), but usually I trust the developer to validate what he wrote with whomever is in charge of the product, allowing the PR to focus on code quality, rather than product quality.
Most of the time.
I think checking out the branch in local and testing if the feature works should be applied for every PR that either fixes a bug, introduces a new feature or is a refactor. It's not that I don't trust my coworkers but I think all humans are fallible and are allowed to miss some things.
What I don't trust is my ability to statically check all possible changes that the code will introduce just by looking at the PR diff.
Sometimes, if the PR is big or contains big UI changes or if I just feel like it. I'm not following any strict rules on that.
I use hub pr checkout command and then test it.
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